Quite often in a micro hydro system you may have a section of pipe that is not at a perfect downhill grade or even goes uphill – this can lead to air getting trapped in these sections and greatly restricting water flow. One way to deal with this problem that the irrigation industry has come up with is these fancy enclosed float valves.
The key specs for this application are the words “continuous” the other type “kinetic” will only let air out initially until the pipe fills with water, then it will not open again until the water and pressure drop below some low value.
A047A-Air-Vent-Install-Guide – Explains the use and need for air release valves
http://www.valmatic.com/brochures/Air_1500.pdf – General info on why air valves are necessary – geared towards large water mains
- Another simpler option if you have a low pressure (but not siphon/vacuum) system is to use a stand pipe vent. This is just a pipe that extends up high enough to allow the air to naturally exit the piping without losing water. For ever 1psi water you need 2.3 feet of height.
After researching for some time it seems Netafim makes the best($$) product.
65ARIS1 – Will let some air in under negative pressure, not as much as the “vacuum relief” types but still some – this can prevent your pipe from imploding under vacuum so may be desired as long as you always have positive pressure during normal operation.
65ARIS1VM Vacuum Guard – will not let air back in under negative pressure – good for systems that have to still operate under negative pressure such as siphons.
The only problem with both of these models is the high price, $140 and $160 list
There are also less expensive made in China versions for $14 – This model will let air in under vacuum. It also lets the air out under pressure which makes it a “continuous” valve. If you need to prevent vacuum operation an external 1/2″ PVC check valve may inexpensively accomplish this. In places where you are using a siphon to pull water over a hill the check valve is definitely necessary. – I have not tested the ability to add a check valve though.